The present invention aims at increasing the use of the resources allocated to telecommunication devices in order to increase the overall performance of the wireless cellular telecommunication network.
To that end, the present invention concerns a method for enabling, in a wireless cellular telecommunication network, at least one mobile terminal to transfer and/or receive data through multiple frequency bands, the at least one mobile terminal being served by a telecommunication device which is able to transfer and/or receive data through at least one frequency band, characterised in that the method comprises the steps, executed by the telecommunication device of:                obtaining at least one mobile terminal carrier aggregation capability of the at least one mobile terminal,        determining a coordinated carrier aggregation capability C of the telecommunication device from the at least one mobile terminal carrier aggregation capability,        transferring the coordinated carrier aggregation capability C to a centralizing device of the wireless cellular telecommunication network,        transferring information related to at least one neighbouring telecommunication device to the centralizing device of the wireless cellular telecommunication network,        receiving, from the centralizing device, information indicating at least one frequency band the telecommunication device has to use for communicating with the mobile terminal,        transferring control signalling to the at least one telecommunication device through the at least one frequency band the telecommunication device has to use for communicating with the mobile terminal.        
The present invention concerns also an apparatus for enabling, in a wireless cellular telecommunication network, at least one mobile terminal to transfer and/or receive data through multiple frequency bands, the at least one mobile terminal being served by a telecommunication device which is able to transfer and/or receive data through at least one frequency band, characterised in that the apparatus is included in the telecommunication device and comprises:                means for obtaining at least one mobile terminal carrier aggregation capability of the at least one mobile terminal,        means for determining a coordinated carrier aggregation capability C of the telecommunication device from the at least one mobile terminal carrier aggregation capability,        means for transferring the coordinated carrier aggregation capability C to a centralizing device of the wireless cellular telecommunication network,        means for transferring information related to at least one neighbouring telecommunication device to the centralizing device of the wireless cellular telecommunication network,        means for receiving, from the centralizing device, information indicating at least one frequency band the telecommunication device has to use for communicating with the mobile terminal,        means for transferring control signalling to the at least one telecommunication device through the at least one frequency band the telecommunication device has to use for communicating with the mobile terminal.        
Thus, the resources allocated to telecommunication devices like home base stations or base stations or relays are used more efficiently. The overall performance of the wireless cellular telecommunication network is then improved.
According to a particular feature, the control signalling indicates at least one frequency band on which data related to the mobile terminal are transferred and which is not allocated to the telecommunication device.
Thus, even if a telecommunication device which serves a mobile terminal has carrier aggregation capability which is lower than the mobile terminal carrier aggregation capability, the mobile terminal can take profit of its ability to transfer and/or receive data through plural frequency bands, since it can transfer and/or receive them to and/or from different telecommunication devices on different frequency bands. Since the control signalling is sent by the serving telecommunication device, this multi-point transmission also called coordinated multi-point transmission is transparent to the mobile terminal.
According to a particular feature, the telecommunication device further transfers carrier aggregation capability C′ of the telecommunication device to the centralizing device.
Thus, the centralizing device can allocate C′ frequency bands to the telecommunication device and the telecommunication device is able to take benefit of its carrier aggregation capability in order to improve the cell throughput without using coordinated multipoint transmission together with neighbouring telecommunication devices.
According to a particular feature, the coordinated carrier aggregation capability C is one of the following items:                the maximum mobile terminal carrier aggregation capability among the obtained mobile terminal carrier aggregation capabilities,        the maximum mobile terminal carrier aggregation capability among a fraction of the obtained mobile terminal carrier aggregation capabilities,        the maximum between a telecommunication device carrier aggregation capability of the telecommunication device and the maximum mobile terminal carrier aggregation capability among the obtained mobile terminal carrier aggregation capabilities,        the maximum between the telecommunication device carrier aggregation capability of the telecommunication device and the maximum mobile terminal carrier aggregation capability among a fraction of the obtained mobile terminal carrier aggregation capabilities.        
Thus, the coordinated carrier aggregation capability appropriately reflects the needs of a given telecommunication device and the mobile terminals it typically serves in terms of number of frequency bands to be allocated to a given mobile terminal. It results in not allocating too many different frequency bands to neighbouring telecommunication devices when it is useless.
The present invention concerns also a method for determining which frequency bands have to be used, in a wireless cellular telecommunication network, to communicate with at least one mobile terminal, the at least one mobile terminal being served by a telecommunication device which is able to communicate with the at least one mobile terminal through at least one frequency band, characterised in that the method comprises the steps, executed by a centralizing device of the wireless cellular telecommunication network, of:                receiving from the telecommunication device, a coordinated mobile terminal carrier aggregation capability C of the telecommunication device,        receiving from the telecommunication device, information related to at least one neighbouring telecommunication device of the telecommunication device,        determining for the telecommunication device and the at least one neighbouring telecommunication device, the at least one frequency band the telecommunication device has to use for communicating with the at least one mobile terminal and the at least one frequency band the at least one neighbouring telecommunication device has to use for communicating with the at least one mobile terminal or another mobile terminal,        transferring to the telecommunication device, information indicating to the telecommunication device, the at least one frequency band the telecommunication device has to use for communicating with the at least one mobile terminal.        
The present invention concerns also a centralizing device for determining which frequency bands have to be used, in a wireless cellular telecommunication network, to communicate with at least one mobile terminal, the at least one mobile terminal being served by a telecommunication device which is able to communicate with the at least one mobile terminal through at least one frequency band, characterised in that the centralizing device comprises:                means for receiving from the telecommunication device, a coordinated mobile terminal carrier aggregation capability C of the telecommunication device,        means for receiving from the telecommunication device, information related to at least one neighbouring telecommunication device of the telecommunication device,        means for determining for the telecommunication device and the at least one neighbouring telecommunication device, the at least one frequency band the telecommunication device has to use for communicating with the at least one mobile terminal and at least one frequency band the at least one neighbouring telecommunication device has to use for communicating with the at least one mobile terminal, or another mobile terminal,        means for transferring to the telecommunication device, information indicating to the telecommunication device, the at least one frequency band the telecommunication device has to use for communicating with the at least one mobile terminal.        
Thus, the resources allocated to telecommunication devices like home base stations or base stations or relays are used more efficiently. The overall performance of the wireless cellular telecommunication network is then improved.
Even if a telecommunication device which serves a mobile terminal has carrier aggregation capability which is lower than the mobile terminal carrier aggregation capability, the mobile terminal can take profit of its ability to transfer and/or receive data through plural frequency bands.
According to a particular feature, the centralizing device further transfers to the telecommunication device at least one information indicating to the at least one neighbouring telecommunication device, the at least one frequency band to be used for transferring data between the at least one neighbouring telecommunication device and the at least one mobile terminal or another mobile terminal.
Thus, the telecommunication device is informed of the type of coordinated multi-point transmission it can perform with the at least one neighbouring device, i.e., on which frequency band multi-point transmissions can be performed, without having to rely on reports from the mobile terminals it serves.
According to a particular feature, the centralizing device receives carrier aggregation capability C′ of the telecommunication devices and the at least one frequency band the telecommunication device has to use for communicating with the at least one mobile terminal and the at least one frequency band the at least one neighbouring telecommunication device has to use for transferring data between the neighbouring telecommunication device and the at least one mobile terminal or another mobile terminal are determined according to the coordinated carrier aggregation capability C of the telecommunication devices and to the carrier aggregation capability C′ of the telecommunication devices.
Thus, the centralizing device can allocate C′ frequency bands to a telecommunication device and the telecommunication device is able to take benefit of its carrier aggregation capability in order to improve the cell throughput without using coordinated multipoint transmission together with neighbouring telecommunication devices.
According to a particular feature, the centralizing device determines for the telecommunication devices a graph of neighbouring telecommunication devices.
Thus, through the graph, the centralizing device has a good global knowledge of the connectivity between telecommunication devices. A link or connectivity between two telecommunication devices will result in a constraint in allocating frequency bands to telecommunication devices. Thus, with an appropriate graph, the centralizing device knows that there is no constraint in allocating frequency bands to two telecommunication devices which are not connected.
According to a particular feature, the centralizing device determines at least one clique for each telecommunication device, a clique comprising the telecommunication device and at least a part of the neighbouring telecommunication devices having a wireless connectivity with the telecommunication device, the telecommunication devices being linked to each other by a wireless connectivity or by a virtual wireless connectivity created between two telecommunication devices which have no wireless connectivity.
Thus, different frequency bands will be allocated to different telecommunication devices of a clique and, in a clique of size X, it will be possible to send and/or receive data to a same mobile terminal from the telecommunication devices belonging to the clique on X frequency bands, if each telecommunication device is allocated a single frequency band. If some telecommunication devices of the clique are allocated more than one frequency band, it will even be possible to send and/or receive data to a same mobile terminal from the telecommunication devices belonging to the clique on more than X frequency bands.
According to a particular feature, a clique of a telecommunication device comprises at most a number of telecommunication devices such that the total number of frequency bands allocated to the telecommunication devices of the clique is equal to the coordinated carrier aggregation capability.
Thus, the connectivity in the graph is limited to what is really needed in each telecommunication device and the number of frequency bands in the system can be minimised or the usage of coordinated multi-point transmission can be optimised for a given number of frequency bands.
According to a particular feature, if the carrier aggregation capability of a telecommunication device is upper than one, the centralizing device duplicates the telecommunication device prior to determining the graph of neighbouring telecommunication devices.
Thus, the allocation of frequency bands to telecommunication devices is simplified since after duplication, all telecommunication devices can be considered as transmitting and receiving on a single frequency band.
According to a particular feature, the at least one frequency band the telecommunication device has to use for communicating with the mobile terminal and the at least one frequency band the at least one neighbouring telecommunication device has to use for transferring data between the neighbouring telecommunication device and the mobile terminal or the other mobile terminal are determined using a colouring algorithm.
Thus, by representing a frequency band by a colour and using a colouring algorithm optimising the number of colours, the number of necessary frequency bands is minimised.
Furthermore, for a given graph connectivity, i.e., for a given configuration of wireless connectivity between telecommunication devices, the number of frequency bands is minimised and better frequency reuse is obtained. On the other hand, for a given number of available frequency bands, a better graph connectivity is allowed, i.e. telecommunication devices have more neighbouring telecommunication devices and coordinated multi-point transmission is optimised.
According to still another aspect, the present invention concerns computer programs which can be directly loadable into a programmable device, comprising instructions or portions of code for implementing the steps of the method according to the invention, when said computer programs are executed on a programmable device.
The present invention also concerns an information storage means, storing a computer program comprising a set of instructions that can be run by a processor for implementing the aforementioned methods in any one of its various embodiments, when the stored information is read by a computer and run by a processor.
Since the features and advantages relating to the computer programs are the same as those set out above related to the methods and devices according to the invention, they will not be repeated here.